Arylboron compounds, cyclization

Similar conditions have promoted five-, six-, and seven-membered ring formations by intramolecular cyclization of arylboron compounds onto ketones (Scheme 31). " Biaryl methanols can be obtained from aryl aldehydes by Rh-catalysed addition of an aryl ring bearing an Al-direcfing group ortho to the activated Cyclization... 

A new synthesis of dibenzoboroles by reductive cyclization of arylboron dibromides opens up access to several derivatives of this ring system (Scheme 6) <1996JA7981>. MonoaryIboron dibromides 61 and 62 were prepared by reaction of the appropriate aryl lithium compound 60 with boron tribromide in hexane. Reductive cyclization of arylboron dibromide 61 with an excess of lithium metal in diethyl ether gave bislithium dibenzoborole complex 63. At the time of writing, compound 63 was the first dibenzoborole dianion to be structurally characterized by X-ray... 

Because many 4-benzylpiperidines are physiologically and pharmacologically active, an efficient route to these compounds was developed <03TL8249>. Cyclization of imines containing an allylsilane with aldehydes in a one-pot reaction resulted in 4-methylenepiperidines in good yields. Heck-type arylation of arylboronic acids with 4-methylenepiperidines afforded the styryl derivatives, which gave the desired piperidines on reduction. 

The cyclization can be carried out with halogenated amines, and substitution products of the new ring systems can also be obtained in the conventional way, by nitration, etc. Similar compounds can be prepared directly by using arylboron dichlorides in place of boron trichloride in the procedure indicated above. The parent borazarene derivatives, with hydrogen attached to boron, can be made from the B-hydroxy compounds with lithium aluminum hydride in the presence of aluminum chloride. N-Alkyl derivatives can be made either by using N-alkyl derivatives of the aminobiphenyls as starting materials, or by N-alkylation of the unsubstituted compounds via their N-lithio derivatives. Apart from their inherent interest, compounds of this type can serve as intermediates in various syntheses. Thus benzocinnolines and 2,2 -dihydroxybiphenyls can be obtained from derivatives of 2-aminobiphenyl. ... 

The first Rh-catalyzed asymmetric tandem cyclization of nitrogen-or oxygen-bridged 5-alkynones with arylboronic acids provided a reliable and practical access to a variety of highly enantio-enriched tetrahydrofurans, which are important units that have been found in numerous natural products and pharmaceutically important compounds (140L2712). 

Other reactions such as alkane dehydrogenation [159, 160], decarbonylation reactions [161], cyclization of alkynoic acids [162,163], three-component coupling reactions of boronic acids, allenes and imines [164], fluorenone synthesis by sequential reactions of 2-bromobenzaldehydes with arylboronic acids [165], and hydrosilylation reactions [166, 167] using cyclometalation compounds as their catalysts have also been reported. 

Lam and coworkers reported that the Ir-catalyzed arylative cyclization of alkynone with arylboronic acid afforded cyclic products [162]. Here, lequiv. of alkynone was reacted with phenylboronic acid (l.Sequiv.) with a catalytic amount of [IrCl2(cod)2] (1.5mol%) and KF (l.Sequiv.) (to act as a base) and lerl-butanol (1.5 equiv.) in toluene at 65 °C and provided the tricyclic compound through arylative cyclization in 72% yield along with the 2 1 adduct in 27% yield (Scheme 11.16). 

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